Organogenesis, Teratogenesis and Malformations

Question 1

How do human embryos attach to endometrial epithelial cells

Answer 1

with local clearance of the ‘barrier’ mucinMUC1

Question 2

What are the reasons that 4/5 menstrual cycles where unprotected sex occurs fails to result in pregnancy

Answer 2

• failed fertilisation
• pre-implantation developmental arrest
• failed implantation

Question 3

What occurs at the end of week 2 in embryology

Answer 3

Inner cell mass splits into 2 layers
• Hypoblast
• Epiblast

Trophoblast gives rise to 2 tissues
• Syncytiotrophoblast
• Cytotrophoblast

2 yolk sacs develop
• Primary yolks sac
• Secondary (or definitive) yolk sac

2 new cavities form
• Amniotic cavity
• Chorionic cavity

Question 4

How is cell fate determined

Answer 4

Determined by onset of expression of specific transcription factors
• These switch genes on/off
• Bind to regulatory region of their DNA
• In this regard some control patterning  eg segmentation of pharyngeal arches and somites of the trunk
• These are known as master genes

Question 5

What is organogenesis

Answer 5

all major organs and organ systems are formed during 3rd – 8th week

Question 6

What are malformations

Answer 6

occur during formation of structures e.g. during organogenesis
Complete or partial absence of a structure or an abnormal structure

Question 7

Disruptions

Answer 7

Morphological alterations of already formed structures defects produced by amniotic bands

Question 8

Deformations

Answer 8

Result from mechanical forces that mould a part of a fetus over a prolonged period of time (clubfoot from compression in the amniotic cavity).Often involve musculoskeletal system

Question 9

Syndrome

Answer 9

Group of symptoms that occur together and have a common (single) cause

Question 10

How do people get down syndrome

Answer 10

Down syndrome is typically caused by what is called nondisjunction.
• Nondisjunction happens when a pair of chromosomes fails to separate during egg (or sperm) formation.
• When that egg unites with a normal sperm to form an embryo, the embryo ends up with three copies of chromosome 21 instead of the normal two.
• The extra chromosome is then copied in every cell as the baby develops.

Question 11

What is Turners syndrome and how does it occur

Answer 11

only 45 chromosomes, missing a sex chromosome (X)
Girls affected
In Turner’s syndrome nondisjunction happens when a pair of sex chromosomes fails to separate during the formation of a sperm (or egg).
• When sperm with no X chromosome unites with a normal egg to form an embryo
• The embryo will have just one X chromosome(X rather than XX). As the embryo grows and the cells divide, the X chromosome will be missing from every cell of the baby’s body

Question 12

What is atrial septal defect

Answer 12

• A birth defect of the heart in which there is a hole in the septum that divides the atria
• This allows oxygen-rich blood to leak into the oxygen-poor blood chambers in the heart
• The proposed mechanisms which this may occur could be from the insufficient formation of the septum secundum or through excessive cell death and resorption of the septum primum.

Question 13

What is Truncus arteriosus

Answer 13

Occurs when the blood vessel coming out of the heart in the developing baby fails to separate completely during development, leaving a connection between the aorta and pulmonary artery
• Oxygen-poor blood and oxygen-rich blood are mixed together
• As a result, too much blood goes to the lungs and the heart works harder to pump blood to the rest of the body.
• Babies with truncus arteriosus have a single common valve (truncal valve) which is often abnormal. The valve can be thickened and narrowed, which can block the blood as it leaves the heart. It can also leak, causing blood that leaves the heart to leak back into the heart across the valve

Question 14

What is Patent ductus arteriosus (PDA)

Answer 14

•A persistent opening between the two major blood vessels leading from the hear

Question 15

Hernia of the diaphragm

Answer 15

Diaphragmatic hernias occur when the diaphragm does not form completely leaving a hole.
• The hole in the diaphragm allows part of the intestine (gut) to move into the chest, which can compress the lungs and can stop them developing properly before birth.

Question 16

Pyloric stenosis

Answer 16

Pyloric stenosis is a condition where the passage(pylorus) between the stomach and small bowel(duodenum) becomes narrower.
• The pylorus passage is made up of muscle, which seems to become thicker than usual, closing up the inside of the passage. This stops milk or food passing into the bowel to be digested.
The cause of stenosis may be an abnormal innervation of the pylorus.

Question 17

Oesophageal Atresia

Answer 17

The upper part of the oesophagus doesn’t connect with the lower oesophagus and stomach. It usually ends in a pouch, which means food can’t reach the stomach.
• It often happens along with another birth defect called a tracheo-oesophageal fistula, which is a connection between the lower part of the oesophagus and the trachea
• This causes air to pass from the windpipe to the oesophagus and stomach, and stomach acid to pass into the lungs

Question 18

Hypospadias

Answer 18

Hypospadias is a birth defect in boys in which the opening of the urethra is not located at the tip of the penis.
• The abnormal opening can form anywhere from just below the end of the penis to the scrotum.
Hypospadias of the glans is influenced by multiple factors, but its direct cause is probably defective canalization of the distal glans plate.
• Openings on the penile shaft represent failures of the urethral folds to fuse completely.